[pro] Default behavior of standard output streams

[Nikodemus Siivola]

FWIW, for CMUCL whole story looks like this (from memory, so take this
with a grain of salt) -- SBCL does the same, unsurprisingly.

There are streams *STDIN*, *STDOUT*, *STDERR*, and *TTY*. If /dev/tty
cannot be opened, *TTY* is simply

  (make-two-way-stream *stdin* *stdout*)

*STANDARD-INPUT*, *STANDARD-OUTPUT*, and *ERROR-OUTPUT* start out as
synonym streams for *STDIN*, *STDOUT*, *STDERR*.

*TERMINAL-IO*, *QUERY-IO* and *DEBUG-IO* start out as synonym streams for *TTY*.

Neither two-way-streams nor synonym streams get buffering of their
own: anything written to them is immediately written to the underlying
stream.

It's not a perfect setup, but it's not half bad, IMO.

Cheers,

 -- nikodemus